Patent GB-754443-A (GB)
Title: Improvements in or relating to colour television receivers
IPC: H04N9/24
Filed: 1954-01-22
Abstract: 754,443. Colour television. GENERAL ELECTRIC CO., Ltd., and BIGGS, A. J. Jan. 20, 1955 [Jan. 22, 1954], No. 1986/54. Class 40 (3). [Also in Group XL (a)] In a colour television receiver incorporating a cathode-ray tube 10 the screen of which, Fig. 2, comprises a repeating sequence of blue, green and red luminous strips 12, 13 and 14 arranged to be scanned with the line direction transverse the strips, means are provided for deriving signals from the screen in response to the scanning of each of the colours and for combining the signals to provide a synchronizing signal to establish synchronizm between the application of component colour signals to the tube gun and the scanning of the corresponding . colours on the screen. In one arrangement, as illustrated in Figs. 1 and 2, metallic strips 15 are superimposed over each luminous strip and connected together in three sets (corresponding respectively to the three colours) from which leads 16-18 are taken out through the tube envelope. In alternative arrangements (not illustrated) three photoelectric cells responsive respectively to blue, green and red light may view the tube screen, or a secondary emission effect may be utilized with a different coefficient for each colour, and the tube incorporating an auxiliary collector electrode. In Fig. 1 the connections from the three sets of metallic strips extend through transformers 23-25 to the high-voltage supply 26, and during scanning, trains of pulses at the same recurrence frequency but differing in phase appear across the transformer secondaries. The three pulse trains are fed via amplifiers 27-29 to relay lines 30-32, which are arranged so that corresponding pulses in each train are brought into coincidence. Delay line 30 is arranged to delay the signal train derived from metal strips 15 corresponding to the blue luminous strips 12 by a period equal to the time taken by the scanning beam to pass across one sequence of the strips 12, 13 and 14, while delay lines 31 and 32 are respectively arranged to delay the signal trains corresponding to the green and red luminous strips by two-thirds and one-third of this period. The three signal trains are then combined to provide a synchronizing signal recurring at the instants of scanning the blue luminous strips. The synchronizing signal thus obtained may then be applied directly to operate a gating circuit 7 connecting a blue signal channel 4 to the tube gun, and through delay lines 33 and 34 having delays respectively equal to one-third and twothirds of the period referred to above to operate gates 8 and 9 connected to green and red signal channels 5 and 6. To ensure the production of a synchronizing signal during reception of black-level signals, the cathode-ray beam may be biased so that it is never quite reduced to zero. Furthermore, to ensure accurate synchronism at the beginning of a line, the scanning beam may be arranged to traverse a small number of metal strips 15 before reaching the screen proper. In an alternative arrangement (not described in detail) the synchronizing signal may be employed to control the rate of scanning of the beam whilst the colour signals are gated to the tube gun in fixed sequence at a steady repetition rate. The luminous strips may comprise differently coloured phosphors or a uniform layer of white phosphor in association with a coloured optical strip filter. The widths of the differently coloured strips may vary to compensate for their differing efficiencies, and the spacing of the strips may be non-uniform to allow for non-linear scanning.